Advances in nanoscience and technology increasingly rely on techniques for fabricating structures comprising features having selected physical dimensions, such as lengths, heights and widths, in the nanometer regime. Methods that have emerged from the microelectronics industry, such as deep UV projection mode lithography and electron beam lithography, are well suited for patterning two dimensional (2D) nanostructures on ultraflat glass or semiconductor surfaces. The limited depth of focus of these approaches, however, makes it challenging, if not commercial unfeasible, to fabricate directly the types of three dimensional (3D) nanostructures that are important for many areas of nanotechnology. To extend the applicability of these methods, indirect approaches of generating 3D nanostructures have been developed with employ repetitive application of steps that involve 2D patterning of sacrificial resists, depositing functional materials, etching or polishing them, and removing the sacrificial layers. These strategies, however, typically require sophisticated facilities and are difficult to implement for structures that demand more than a few layers. As a result of these well recognized limitations, there is presently a demand for high throughput, low cost fabrication methods capable of generating a wide variety of nanostructures.
Recently, new methods of fabricating 3D nanostructures have been developed. Methods based on colloidal sedimentation, polymer phase separation, templated growth, fluidic self-assembly, multiple beam interference lithography, and various approaches based on printing, molding, and writing are all useful for building different classes of 3D nanostructures. Nevertheless, these techniques have certain limitations in the geometries, physical dimensions and sizes of patterns that they can generate. For example, two-photon lithography can produce an impressive variety of structures, but its serial operation makes it difficult and labor intensive to pattern large substrate areas or to generate large numbers of structures.
Holographic and photolithographic methods also provide useful methods for fabricating structures. Exemplary methods for generating patterns and structures are described in “Fabrication of photonic crystals for the visible spectrum by holographic lithography,” Campbell, M., Sharp, D. N., Harrison, M. T., Denning, R. G. and Turberfield, A. J., Nature, Vol. 404, pgs. 53-56 (2000) and “Generating ≈90 nanometer features using near field contact mode photolithography with an elastomeric phase mask,” Rogers, J. A., Paul, K. E., Jackman, R. J. and Whitesides, G. M., J. Vac. Sci. Technology. B, Vol 16(1), pgs, 59-68 (1998), which are hereby incorporated by reference in their entireties to the extent not inconsistent with the present description.